Mega refactor: package layout, typed events, tests, docs, tooling

[s2x]

Summary

Senior-pass refactor of the whole project. The 283-line main() is gone; the program is now split into 4 small packages with full test coverage and matching tooling.

Package layout

Package	Responsibility
internal/event	Typed Envelope / AssistantMessageEvent / ToolCall / Result structs replacing every map[string]any assertion.
internal/render	Renderer state machine with named ANSI constants and a tiny printf helper.
internal/pi	Subprocess lifecycle (Start / Events / Close / Kill) wired to context.Context. BuildArgs extracted for testing.
internal/cli	Flag parsing + event-loop orchestration; structured exit codes (0/1/2/130); --version.

main.go is now a ~10-line entrypoint: installs signal.NotifyContext(SIGINT, SIGTERM) and delegates to cli.Run.

Tooling aligned with decodo-coding-tools

• .golangci.yml v2 — govet, staticcheck, unused, ineffassign, errcheck, dupl + gofmt
• Makefile — fmt, vet, staticcheck, lint, lint-fix, tidy, check, build, install, clean, test
• CI split into independent jobs: lint, fmt-check, govet, staticcheck, tidy, test (ubuntu + macOS matrix), build (gated on the above, embeds short SHA via -ldflags)

Other senior touches

• LICENSE (MIT)
• README with usage, flags table, exit codes, dev commands
• Graceful shutdown via signal.NotifyContext — no orphaned pi child on Ctrl+C
• Removed dead State.String, dead start-event handlers, magic numbers pulled into named constants
• All interface{} replaced with any

Tests

34 tests across 4 packages, all passing under -race. Coverage:

• event: envelope parsing for response/text_delta/toolcall_end/tool_execution_end, Result.SummaryText nil/empty cases
• render: all section transitions, ToolCall with/without args, ToolExecStart bash vs non-bash, ToolExecEnd success/error/truncation, JSON without HTML escaping, newline injection
• pi: BuildArgs defaults, with session, full options, omits empty fields
• cli: agent_end stops with 0, error envelope stops with 1, response failure stops with 1, text_delta renders, tool_execution_end renders, tool_call_end with/without ToolCall

Test plan

• go test -race -count=1 ./... — 34 passing
• gofmt -l . — clean
• go vet ./... — clean
• staticcheck ./... — clean
• golangci-lint run — clean
• go build -ldflags '...' -o pi-stream . — produces working binary
• Manual: ./pi-stream --version prints version
• Manual: ./pi-stream --model "GLM 5.1" -t bash "..." renders correctly